It is well known to remotely control a travelling body to travel by a remote controller (base device). A video camera is mounted on the travelling body, and image signals from the video camera are transmitted to the remote controller, and an operator operates the remote controller while looking at a monitor display accompanying the remote controller. Remote control signals from the remote controller are transmitted to the travelling body to cause the travelling body to move forward or backward, or to turn.
Systems for transmitting the image signals and the remote control signals include a wireless system and a wired system. A wired system is mainly adopted when the travelling body is used in a place where radio waves are not easily received, such as in a building with winding passages or under water.
In rescue operation or exploration, the work site may be within a building, and the operator of the controller may have to perform operation from a distance of more than 100 meters, or sometimes as far as one kilometer, due to poison, radiation, explosion risk, or the like which prevents the operator from getting close to the site. In these cases, wired travelling bodies are mainly used.
In the wired system, the travelling body and the remote controller are connected by a long cable, and a signal transmission wire is embedded in the cable.
In the wired system, a reel for winding the cable is generally installed in the travelling body. This is because, if the reel is installed in a base station, the travelling body has to draw out the cable from the reel in the base station, and the burden is great.
However, in the case where the reel is mounted on the travelling body as described above, there is a problem that, because a thin long cable is wound around the reel, the cable may be slackened and be caught at a part of the travelling body or the cable may get tangled, becoming unable to transmit signals, and as a result, the travelling body may become immobilized.
Japanese Patent Nos. 4630908, 5432419, and 5426049 disclose a reel device mounted on crawler-type travelling body. The reel device includes a reel around which the cable is wound, a motor connected to the reel, a rotary encoder (rotation sensor) for detecting rotation of the reel, and a motor controller.
According to the disclosures of the three referenced Japanese patents, the motor controller basically controls the motor in the following manner.
When the travelling body is moving (forward) in the direction away from the remote controller (base station), and the rotary encoder is outputting a pulse signal indicating rotation in the unreeling direction of the reel, the motor is made free, allowing the cable to be smoothly unreeled from the reel device, thereby preventing the cable from becoming too tense as to obstruct the forward travelling of the travelling body.
Also, when the travelling body is moving (backward) in the direction of getting closer to the remote controller, the motor is driven to reel the cable onto the reel, and the cable is prevented from being slackened.
However, the basic control as described above alone may cause an inconvenience. For example, when the travelling body is moving forward, the motor is freed and the cable is unreeled. In this state, if the travelling body suddenly stops, the reel keeps rotating due to inertia, and the cable is unreeled more than necessary and is slackened.
Accordingly, in Japanese Patent No. 4630908, an accelerometer for detecting the acceleration in the forward/backward direction is installed in the travelling body, and when the travelling body suddenly stops while moving forward, the cable is reeled by the motor controller driving the motor and causing the reel to rotate in the reeling direction, in response to the acceleration in the backward direction detected by the accelerometer.
Moreover, the basic control as described above alone may also cause inconveniences as follows. For example, after the travelling body completes climbing up stairs, the front side of the travelling body is suddenly pulled downward by gravity, and the attitude is suddenly changed from an inclined attitude to a horizontal attitude. At this time, due to the sudden change in the attitude of the travelling body, the reel is pulled by the cable and is rotated at a great speed, and the cable is unreeled at a great speed. The reel keeps rotating at a great speed due to inertia after the landing of the travelling body. As a result, the cable is slackened, and this slackened portion may get entangled with the reel rotating in the unreeling direction, or may be spread near the reel in a disorderly manner, or may get caught at a part of the travelling body, thereby immobilizing the travelling body and preventing it from returning.
Accordingly, in Japanese Patent Nos. 5432419 and 5426049, an accelerometer for detecting acceleration in the vertical direction is installed in the travelling body, and when the attitude of the travelling body is suddenly changed, the motor controller drives the motor and rotates the reel in the reeling direction in response to acceleration information from the accelerometer to thereby reel the cable.